In preparation for production of a subterranean formation, a wellbore is drilled, penetrating the subterranean formation. In order to stabilize the wellbore, a casing is run into the wellbore. Generally, for effecting isolation or substantial isolation, of one or more zones of the subterranean formation from formation fluid being produced from another zone of the subterranean formation, zonal isolation material, such as cement, is provided within the wellbore, between casing and the subterranean formation.
Due to a number of reasons, zonal isolation may not be achieved. Less than desirable zonal isolation may result from improper setting of zonal isolation material (for example, cement) within the wellbore, shrinkage of the zonal isolation material as it sets up, fluid migration into the annulus before the zonal isolation material has set up, water escaping from the zonal isolation material as it is setting up, and the presence of remaining drilling mud within the annulus. As well, once the zonal isolation material has been set within the wellbore, the zonal isolation material may be subjected to a variety of mechanical and thermal stresses that may lead fractures, cracks, and/or debonding of the zonal isolation material from the casing and/or the subterranean formation. Such failure, manifested in the formation of channels and microannuli, may lead to loss of zonal isolation, resulting, for example, in the undesirable migration of formation fluids between zones within the subterranean formation. This may lead to lost production, costly remedial operations, environmental pollution, hazardous rig operations and/or hazardous production operations. Compromised sealant (cement) may render the wells unsuitable for storing crude oil or natural gas, injecting water or gas for pressure maintenance and enhanced recovery. Compromised sealant (cement) in the casing by the wellbore annulus also renders wells unsuitable for disposing of waste water or gases such as hydrogen sulphide and carbon dioxide, therefore rendering these wells unsuitable for carbon sequestration.
Existing attempts to mitigate failure to achieve zonal isolation relate to improving the characteristics of the zonal isolation material such that the zonal isolation material maintains its integrity even when subjected to the various mechanical and thermal stresses. As well, sealants, containing particles, e.g., cement, have been developed for injection into narrow pathways to remediate the created channels and micro-annuli. Neither of these solutions have been completely adequate. For example, in some cases, the narrow pathways present excessive resistance to flow of an injected sealant, while still permitting flow of a formation fluid (such as a gas) that is sufficiently compressible and has sufficiently low viscosity.